* {
    margin: 0;
    padding: 0;
}

header {
    display: block;
    margin: 0 auto;
    width: 500px;
    text-align: center;
}

header h1 {
    font-family: Arial, Helvetica, sans-serif;
    font-size: 60px;
    font-weight: bold;
    margin-top: 20px;
    margin-bottom: 20px;
}

header #newgamebutton {
    width: 100px;
    padding: 10px;
    background: #8f7a66;
    font-family: Arial, Helvetica, sans-serif;
    color: white;
    border-radius: 10px;
    text-decoration: none;
}

header #newgamebutton:hover {
    background: #9f8b77;
}

header p {
    font-family: Arial, Helvetica, sans-serif;
    font-size: 25px;
    margin: 20px auto;
}

#grid-container {
    width: 460px;
    height: 460px;
    padding: 20px;
    margin: 40px auto;
    background: #bbada0;
    border-radius: 10px;
    position: relative;
}

.grid-cell {
    width: 100px;
    height: 100px;
    border-radius: 6px;
    background: #ccc0b3;
    position: absolute;
}

.number-cell {
    width: 100px;
    height: 100px;
    border-radius: 6px;
    line-height: 100px;
    font-family: Arial, Helvetica, sans-serif;
    font-size: 50px;
    font-weight: bold;
    text-align: center;
    position: absolute;
}

#gameover {
    background-color: rgba(0, 0, 0, .3);
    color: white;
    font-family: Arial, Helvetica, sans-serif;
    font-size: 60px;
    width: 100vw;
    height: 100%;
    text-align: center;
    /* display: flex; */
    justify-content: center;
    align-items: center;
    position: absolute;
    top: 0;
    left: 0;
    display: none;
}

#back {
    width: 100px;
    padding: 10px;
    background: #8f7a66;
    font-family: Arial, Helvetica, sans-serif;
    color: white;
    border-radius: 10px;
    text-decoration: none;
    position: absolute;
    right: 300px;
    bottom: 300px;
    text-align: center;
}

#back:hover {
    background: #9f8b77;
}